Earth-Like Planet Found

European astronomers said Monday that they had found what might be the best candidate for a Goldilocks planet yet: a lump of something about 3.6 times as massive as the Earth, circling its star at the right distance for liquid water to exist on its surface — and thus, perhaps, to host life, as we narrowly imagine it.

An illustration of what the planet orbiting the Sun-like star HD 85512b might look like.

The planet, known as HD 85512b, is about 36 light-years from here, in the constellation Vela. It orbits its star at about a quarter of the distance that Earth circles the Sun, taking 58 days to make a year. That distance would put it in the star’s so-called habitable zone, if the planet is rocky and has some semblance of an atmosphere — “if everything goes right and you have clouds to shelter you,” as Lisa Kaltenegger of the Harvard-Smithsonian Center for Astrophysics and the Max Planck Institute for Astronomy in Heidelberg, Germany, summarized it. 

Astronomers cautioned, however, that it would take years and observations from telescopes not yet built before those assumptions could be tested and a search for signs of life could be undertaken.

Neither humans nor their robot helpers are likely to be dispatched toward Vela anytime soon. But the finding did vault HD 85512b to the top of a list of the handful of Goldilocks candidates. 

The Vela planet was part of a haul of more than 50 new exoplanets — as planets around other stars are called — discussed in a news conference on Monday hosted by the European Southern Observatory. They are the newest fruits of an eight-year observing program by astronomers based at the University of Geneva and led by Stephane Udry and Michel Mayor, working from a telescope at the European Southern Observatory in Chile. About 16 of them are so-called super-Earths, with masses less than 10 times the Earth, further encouraging astronomers that they are on the verge of finding planets like ours. A pair of papers — one with Dr. Mayor as lead author and the other with Francesco Pepe, also of Geneva, as lead author — have been submitted to Astronomy and Astrophysics, describing the planets. 

The Geneva astronomers used a sensitive spectrograph known as Harps (an acronym for High Accuracy Radial velocity Planet Searcher) to detect wobble in the stars’ motions as planets swung around them. The wobble technique, however, only reveals the masses of exoplanets. Without further information like the size — which NASA’s Kepler satellite, also in the exoplanet business, measures by seeing the shadows of planets as they cross in front of their stars — or the composition, the astronomers cannot say for sure whether the Vela planet is made of rock, steam, iron, diamonds or something else. Nor can they tell what, if any, 

atmosphere it has. Kepler will be of no help because its gaze is fixed on a different swath of sky. 

The star that the Vela planet circles is known as HD 85512, or Gliese 370, after Wilhelm Gliese, a German astronomer. The star is orange, about two-thirds as massive and about an eighth as luminous as our Sun.

A study led by Dr. Kaltenegger, Dr. Pepe and Dr. Udry concluded that HD 85512b was potentially habitable if it had more than a 50 percent cloud cover. 

Dimitar Sasselov of the Center for Astrophysics, who has followed this work but is not part of the team, said that Dr. Kaltenegger and her colleagues made reasonable assumptions. He called the result “very solid” and “a major step in the right direction.” 

Others were less impressed by the case for habitability. Sara Seager of the Massachusetts Institute of Technology noted that Dr. Kaltenegger’s model atmospheres were limited to water, carbon dioxide and nitrogen, like the Earth. 

“A very terracentric view,” she said in an e-mail.

Dr. Seager said, “Would I bet $1 that this is a habitable planet? No. If I had a space telescope that could look at the atmosphere, would I point to the planet? Yes.” 

http://www.nytimes.com/2011/09/13/science/space/13planet.html?_r=1&hp